What is the cause of the nodule on this lady's shin?
Dr Keith Hopcroft explains how a simple test led him to the correct diagnosis in this patient
This 35-year-old woman presented in a very anxious state. She had been aware of a small lesion on her leg for a few months. But it hadn't really bothered her, until a work colleague had recently been diagnosed with a melanoma.
The nodule was on her right shin and wasn't painful or itchy. It had appeared spontaneously and there weren't any similar lesions elsewhere. She had an unremarkable past medical history and, in particular, she had not suffered any previous dermatological problems. Her colleague's experience had clearly scared her though – and she was requesting referral for a private dermatological opinion before I'd had a chance to take a proper look at the lesion.
Examination revealed a 0.5cm firm, non-tender brownish-red nodule on her shin. The surrounding skin was normal and there was no regional lymphadenopathy.
It was a fairly nondescript lesion and didn't have any alarming features. The temptation in this situation is to simply reassure the patient that this is ‘nothing to worry about', even if we can't provide a specific label.
In this case, though, it was clear that the patient was after a dose of certainty. And my best guess was that this was a histiocytoma.
- Malignancy such as melanoma or basal cell carcinoma
- Sebaceous cyst
- Keloid scar.
A patient's anxiety can be infectious and so I illuminated and magnified the lesion and took a long, hard look at it. A sun-exposed site always raises the possibility of malignancy, but there were none of the characteristic features of a melanoma, nor even of the rather less alarming basal cell carcinoma.
The nodular feel in a hairy area raised the possibility of a sebaceous cyst – but it was an atypical position and an odd colour for this diagnosis.
A small keloid scar was another differential, but she couldn't recall any episode of trauma in that area.
So I thought that my gut instinct was likely to be correct – it was the right morphology in the right position to be a harmless histiocytoma.
The hidden clue
I was obviously less convincing than I thought – despite me giving her a specific diagnosis, with an impressive sounding name, she remained anxious and sceptical. It was then that I recalled a trick I'd learned a year or so previously on a dermatology study day.
Histiocytomas are tethered to the underlying fibrous tissue – so squeezing the skin to the sides of the lesions produces a characteristic dimple. I demonstrated this, to my immense satisfaction.
Getting on the right track
I may have felt satisfied by this point, but my patient remained keen on using her private health insurance to have the nodule removed. So I referred her, and was gratified to receive the histology a week or two after an excision biopsy – it was a histiocytoma.
Dr Keith Hopcroft is a GP in Laindon, Essex